Copper, although present in the body in small amounts, is essential for life. In certain diseases, copper metabolism is abnormal, however, the mechanisms of copper homeostasis are poorly understood. An important potential cause of abnormal copper absorption may contribute to the increased hepatic copper which occurs in Wilson's disease and chronic cholestasis. Alternatively, copper absorption may be impaired in diseases of the small intestine, such as adult celiac disease. Studies of copper absorption and metabolism are being conducted using the NIH whole body counter systems using simultaneous oral administration of 64Cu and intravenous administration of 67Cu. In-vivo gamma-ray measurements of the liver and thigh areas, total body retention, and activity in blood and excreta will provide information about absorption and retention of copper in normal subjects and in patients with disorders of copper metabolism. It is hoped that such studies will provide insights into the normal metabolism of copper on the mechanisms of abnormal copper metabolism which result in disease.